Method of electroplating fine wire of low elastic limit



Feb. 21, 1950 c. LUKE 2,497,894

METHOD OF ELECTROPLATING FINE WIRE OF LOW ELASTIC LIMIT Filed Oct. 14,1944 2 Sheets-Sheet l Y i J 2 Sheets-Sheet 2 C. LUKE METHOD OFELECTROPLATING FINE WIRE OF LOW ELASTIC LIMIT W W W J Feb. 21, 1950Filed 001;- 14, 1944 Patented Feb. 21, 1950 METHOD OF ELECTROPLATINGFINE WIRE OF LOW ELASTIC LIMIT Clare Luke, Berrien Springs, Mich,assignor to National-Standard Company, a corporation of MichiganApplication October 14, 1944, Serial No. 558,697

6 Claims. (01. 2o4-2s) This invention relates to a method of handlingwire of fine diameter and low elastic limit.

Wire is customarily stored and transported on spools on which the wireis wound in a plurality of overlapping courses, each extending from oneend of the spool to the other. In any treatment the wire must be takenoff of one spool and placed upon another. In handling very fine wires,particularly of metal such as copper, the mere transfer from one spoolto another is a matter of some difiiculty and is likely to lead toconsiderable breakage. For example, an annealed copper wire having adiameter of 0.005 inch and having an elastic limit of 20,000 lbs. persq. in., will stretch beyond its elastic limit if the tension upon itexceeds A lb. Even with a similar wire of 0.020 inch diameter, thetension cannot exceed 4 lbs. The present invention provides a method bywhich wires of these small diameters and low elastic limit maysuccessfully be handled and even passed through a series of bathswithout being stretched beyond their elastic limits.

This is accomplished by mounting the takeoff spool in such manner as tofeed wire at a predetermined level, passing the wire under tension belowits deforming tension in a catenary path of extremely small depth to atake-up spool or drum. The wire may in its path be permitted to fall, tothe extent of the depth of the catenary, into one or more baths whichpreferably include a cleaning bath, a pickling bath, a plating bath, andone or more washing baths. Plating is preferably by electrodeposition.It is of course impracticable to employ solid contacts within thecatenary when dealing with wires of such small strength. Current is,therefore, passed through the wire by contacts which include one ormoreof the baths and oneof the spools, preferably a power driven take-upspool or drum.

By means of the invention it has been possible for the first time toelectroplate copper wire as small as 0.005. inch in spool lengthunbroken sections. This is of great value in the electric in dustrywhere thecopper wires are to be coated with a rubbery insulation,particularly a sulfur containing elastomer insulation which is adverselyaffected by contact with copper.

I The invention is illustrated in the drawings in which Fig. 1 is a sideelevation of an apparatus suitable for practicing the invention; Fig. 2is a plan view; Fig. 3 is an enlarged sectional side Fig. '4' is adiagrammatic enlarged view of the Q modified form of overflow; Fig. 6 isa fragmentary wire; F -.3 5,? t an v r e end levationpr plan Viewshowing a modified system. incorporating several wires; and Fig. 7 is adiagram of the electric circuit.

The apparatus comprises a suitable mounting upon which a let-off spool(not shown) is carried. A series of tensioning and spacing members 22 ofwhich only one is illustrated are provided adjacent the spool tomaintain the wire 20 at substantially a predetermined vertical position.The wire 20 passes through a series ofbaths which will be laterdescribed to a power driven capstan Wrapped several times and from whichit is passed to a take-up spool 23. It will be noted that between thespacing or tensioning devices 22 and the point of contact with thecapstan l0 the wire is suspended in a catenary of very small depth. With0.005 inch annealed copper wire the catenary should not be deeper thanapproximately /2 inch and is preferably about A; inch. For 0.020 wirethe depth of the catenary may be somewhat greater.

The series of baths comprises an alkali cleaning bath 2 preferablycontaining an alkali cyanide solution; a cold water rinse 3, an acidpickle bath 4, a water wash 5, a plating bath 6, a cold water wash 1,and a hot water wash 8. Each of the baths is constantly supplied withfluid which overflows at the edges of the baths as shown in Figure 3.This overflow is, except in the case of the cold wash water, recycled bymeans of pumps H. The surface tension of the liquid in each bath formsan inverted meniscus l2 at the overflow l3 and the wire passes into andout of each bath through such a meniscus. In somein which direction ofcurrent flow is indicated by arrows, plating current from a directcurrent source 24 passes through a wire 25 to electric contacts b in theplating bath 6; the current actually passing into the electrolytethrough the anode I5. The current splits in the bath 6 as it passes intothe wire 20, part of the current passl0 around which the wire is Such aslotted ing through the capstan l0 and the wire 26 to an ammeter 21 anda variable resistance 28, thence through the wire 29 as to the source ofcurrent. The remainder .of the current passes through the wire 20 to thebath 2, through the electrolyte to theelectrodes M. from which it passesthrough a wire 30, an ammeter 3|, a variable resistance 32, and throughthe wire 29 to the source of current. The ammeters 21 and 3| indicatethe current levels in the baths 6 and 2. respectively, permitting theoperator to maintain proper distribution of current to the two branchesof the circuit by means of the variable resistors 28 and 32. In view ofthe current flow above described, it is clear that the electrode IS inthe bath 6 is positively charged, while the capstan l and the electrodesM are negatively charged.

The wire may be withdrawn from the let-off spool at a speed of 400 ft.to 500 ft. per minute. A suitable total tension is less than /4 lb. Thecleaning bath is designed to remove saponiflable impurities and suitablyis an alkali cyanide, for example one containing 2 oz. of sodium cyanideper gallon. It is preferably heated to a temperature of the order of 140F., as, for example, by steam coils 9. Overflow liquid is recycled bythe pump ll beneath the surface of the bath, it being introduced nearthe bottom. An air jet l-6 having a small opening immediately above thewire and directed vertically downward removes cleaning liquid carriedfrom the bath by the wire. An enlarged jet is shown in Figure 3. Theamount of liquid carried from a bath by a small wire is extremely greatand losses because of this would be sufficient to render the processunduly expensive, if the liquid were permitted to be lost. Inconventional plating baths the liquid is removed by wipes of cloth orother material, but in the present system such methods cannot beemployed because of the tension necessaril imposed. The air blastsatisfactorily removes the liquid from small wires and the wires feeldry to the touch after passing through the air. Similar air jets areprovided after each bath. In each case the jet is within the areabounded by the sump below the bath. Each bath, except the cold waterwashes, is provided with a sump II, which need not be further described.

The wire passes from the first air jet IE to the cold water rinse,thence under another air jet [6 into the acid pickle 4. This acid ispreferably hydrochloric which is ordinary commercial hydrochloricdiluted with from 1 to 4 parts of water. Overflow acid is recirculatedby the pump Ha. The edges of this tank, as is the case with all of theother tanks, should have substantially the same level so that theoverflows in all cases are within the catenary formed by the wire 25.The wire, after cleansing and neutralization in this bath, passes underanother air jet I 6 and into the water wash 5, into another jet l6 andinto the plating bath 6.

For tin plating a fluoride tin bath of conventional composition may beemployed. A suitable amperage is 500 per square foot but this may bevaried to as low as 20 or as high as 1800. The amount of platingrequired for use in electric wiring is not great, generally being about0.00002 inch. At 500 ft. per minute, and 500 amperes per square foot,the wire will acquire this coating in 9 feet of travel. The preferredbath has about this length.

As shown in the drawing, the electrode I5, which ma be the bottom of thebath or may be a tray secured above the bottom of the bath, is slopeddownwardly from the center in each direction. The amount of this slopeis such as to equalize the voltage drop through the solution. It must ofcourse be varied with variations in the size of the wire and, for thatreason, is preferably hinged at la to permit "adjustment.

The plating fluid is heated in the sump by steam coils 9apreferably to atemperature in the neighborhood of F. The liquid is circulated by a pumpI lb and reintroduced at the bottom of the tank 6.

The wire passes from the plating bath under another air jet 16 throughthe overflow of the cold water wash 1, under another air jet [6 throughthe overflow of the hot water wash 8, under another air jet I6 and tothe capstan Ill. The hot water wash is maintained at a temperaturearound F. by steam coils 9 in the sump. Overflow is circulated to thebottom of the tank by the pump Hc. This hot water bath serves to assistthe final air jet l6 by heating the wire to a point where any remnant ortrace of water is evaporated.

The capstan I0 is of conventional tapered shape and is so spaced thatits take-up level is substantially the same as the level produced by thetensioning and spacing devices 22. The capstan is driven by a motor at apredetermined speed and the wire then passes to the spool 23 which isdriven in conventional manner by a slipping belt under constant tensionso that there is no slack in the wire or any superimposed tension beyondthe desired amount.

It will be observed that the wire 25 is suspended in a catenary of smalldepth, which catenary is constantly changing as the wire advances andwhich maintains its shape. The catenary passes through the overflow ofeach of the baths, all of its contact with the liquids being confined toa layer of liquid having the depth of the catenary. As already stated,it is preferred to use a catenary having a depth of approximately A incheven over a space of approximately 30 feet.

Make-up water is supplied to the cold water tanks in any suitablefashion, as from overhead pipes 18.

The product produced b the herein described method is characterized bythe fact that all of the plated metal occupies the same position withrespect to underlying metal and to the center of the wire which itoccupied at the time it was deposited. If it were attempted toelectroplate a wire of the type here described by ordinary methods, thewire would stretch as much as 40-50% of its length so that depositedmetal would be displaced longitudinally and vertically with respect toits initially occupied position.

A system may be employed with more than one wire, in which case acapstan may be employed for each wire. Such an instance is shown byFigure 6, in which wires 25a, 25b and 250 are respectively driven bycapstans lUa, lflb and H10. It will be seen that the distance betweeneach capstan and the plating bath 0 will be difierent. This iscompensated for by including a separate voltage regulator with each wireso that they may be separately adjusted.

The invention is primarily applicable to wires having a cross-sectionalarea not substantially more than 0.0004 square inch, and elastic limitsof not substantially more than 20,000 lbs. per square inch.

The foregoing detailed description has been given for clearness ofunderstanding only, and no unnecessary limitations should be understoodtherefrom.

What I claim as new, and desire to secure by Letters Patent, is:

1. The method which comprises withdrawing a metal wire having across-sectional area not substantially greater than 0.0004 square inchand an elastic limit of not substantially more than 20,000 lbs. persquare inch from a let-oil spool while maintaining the wire at apredetermined vertical position, passing the wire in catenary suspensionof a depth not substantially exceedin one inch below said verticalposition and at a speed of at least several hundred feet per minute to arotating power driven take-up through the overflow meniscuses of atleast one aqueous liquid bath, which is a metal plating bath, said wirebeing suspended between only two points and being free from contact withany solid body therebetween, supplying current to said wire during suchpassage through connections including only said bath and said take-up,while maintain- :ing upon the wire a tension less than that required tostretch it beyond its elastic limit, and removing substantially allliquid from the wire at the exit of each bath.

2. The method of electroplating annealed copper wire having across-sectional area not substantially greater than 0.000025 square inchwhich comprises passing the wire at a speed of about 400-500 feet perminute from a first support through the overflow meniscuses of a seriesd of aqueous baths, at least one of said baths being a plating bath andthe others being cleaning baths, to a rotating power driven take-up,maintaining the wire out of contact with any solid body in a freesuspension having a depth of not over one-half inch and under a tensionof not more than one-fourth pound during such passage, and supplyingelectric current to said wire during such passage by means ofconnections including only said baths and said take-up.

3. The method which comprises withdrawing annealed copper wire having across-sectional area not substantially greater than 0.000025 square inchfrom a let-off spool while maintaining the wire at substantially apredetermined vertical position, passing the wire at a speed of about400-500 feet per minute to a rotating power driven take-up through theoverflow meniscuses of a series of overflowing baths while maintainingupon the wire a tension not exceeding onefourth pound, at least one ofsaid baths being a plating bath and the others being cleaning baths,supplying electric current to said wire during said passage by means ofconnections including only said baths and said take-up, and maintainingsaid wire free from contact with any solid object other than the let-oilspool and the take-up.

4. The method of electroplating wire of low elastic limit having across-sectional area not substantially greater than 0.0004 square inchwhich comprises advancing the wire at a speed of at least severalhundred feet per minute in a suspension of depth not substantiallyexceeding one inch from a first support through the overflow meniscus ofat least one aqueous liquid bath which is a metal plating bath to asecond support which is a rotating power driven take-up whilemaintaining the wire at a predetermined vertical position and free fromcontact with any solid body other than said first suport and saidtakeup, introducing electroplating current to said wire from said bathand removing said current from said wire through one of said supportsand maintaining a tension upon the wire insufl'icient to stretch itbeyond its elastic limit.

5. The method of electroplating wire of extremely small cross-sectionalarea and low elastic limit which comprises passing the wireprogressively, at a speed of at least several hundred feet per minutewhile maintained in a substantially catenary suspension of a depth notsubstantially exceeding one inch and free from contact with any solidobject, through a series of baths, at least one of said baths being anaqueous plating electrolyte and the remainder of said baths beingcleaning baths, and said baths having overflow portions with themeniscuses thereof within the catenary, to a driven take-up, supplyingelectric current to said Wire during such passage by means ofconnections including only said baths and said take-up, collecting theoverflow from each bath in a sump and returning it to the bath, removingliquid carried by the wire from each bath by means of a blast of airdirected upon the wire to its appropriate sump, and collecting the wireupon the take-up.

6. The method of treating a wire of extremely small cross-sectional areaand low elastic limit which comprises passing the Wire at a speed of atleast several hundred feet per minute in a substantially unimpededcatenary path of a depth not substantially exceeding one inchprogressively through the overflow meniscuses of overflowing liquidbaths, at least one of said baths being a plating bath and the othersbeing cleaning baths, to a take-up, supplying electric current to saidwire during said passage by means of connections including only saidbaths and said takeup, and maintaining said wire free from contact withany solid object while passing in said path.

CLARE LUKE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,068,411 Chubb July 29, 19131,068,412 Chubb et a1 July 29, 1913 1,117,240 Presser Nov. 17, 19141,210,663 Mace et al Jan. 2, 1917 1,513,696 Demel Oct. 28, 19242,075,332 Antisell Mar. 30, 1937 2,093,238 Domm Sept. 14, 1937 2,370,973Lang Mar, 6, 1945 OTHER REFERENCES Metal Industry, Jan. 21, 1944, pages43, 44.

